In article <199411041533.HAA01434 at net.bio.net> kdelgert at vt.edu (Klaus D. Elgert) writes:
> A question arose in our graduate level immunology course. "How do
>macrophages distinguish between self and non-self?" Macrophages are
I think there are two halves of your question: (1) How do macrophages
endocytose foreign rather than self antigen and (2) how do they present
foriegn material rather than self after endocytosis. The short answer
is, they do not differentiate. This is true particularly at the level of
presentation: self and foreign antigens are presented more or less at
random (i.e. if an antigen has the appropriate motifs and the other
caveats are met - cleavage, etc - then that epitope will be presented on
MHC molecules. The discrimination here is at the level of the TcR;
although self-antigen is presented by macrophages, the T cells simply do
not recognize it. (Well, it isn't "simple," I guess.)
As far as endocytosis is concerned, there is not very precise
differentiation here between self and non-self antigens. There is some,
however. As well as the opsinizing effects of antibody and complement,
there seems to be some recognition of different lipids. I can't recall
the whole story on this, but for example during apoptosis there appears
to be alterations of the cell membrane, with a loss of the normal
assymetry of the membrane; the normally hidden lipids act as opsinins and
enhance phagocytosis. This probably is part of the red cell situation
you mentioned. I believe there may be other opsinins which are exposed
or prodced during apoptosis and probably other physiological states.
Hope this helps.
Ian
--
Ian York (york at mbcrr.harvard.edu)
Dana-Farber Cancer Institute, 44 Binney St., Boston MA 02115
Phone (617)-632-4328 Fax (617)-632-2627